1. Field of the Invention
The present invention relates to an occupant protecting device for use in motor vehicles for protecting occupants sitting on seats of a motor vehicle in the event of a collision, and more particularly to an occupant protecting device for a motor vehicle, which inflates an air-bag system reliably to protect occupants in the event of a collision.
2. Description of the Related Art
FIG. 1 is a block diagram showing an example of a conventional occupant protecting device for use in motor vehicles.
In the figure, an acceleration sensor 1 senses an acceleration signal of a vehicle which is generated in the event of a collision with another vehicle or the like. A signal processor 2 includes an integrator for integrating the acceleration signal output from the acceleration sensor 1. The acceleration signal shows a waveform representing the collision. A comparator 3 determines whether or not the output signal of the signal processor 2 exceeds a preset level so as to produce a trigger signal when it exceeds the preset level. A one-shot multi-vibrator or drive circuit 4 latches a trigger signal from the comparator 3 for a preset period of time, and continuously produces a drive signal during the preset period. An ignition device 5 which forms a primary portion of the occupant protecting device, operates to fire in response to a drive signal from the one-shot multi-vibrator 4. When the ignition device 5 is triggered to inflate an air bag or bags and/or to strain a seat belt or belts.
In the occupant protecting device thus constructed which utilizes the integration value output from the signal processor 2, the comparator 3 judges whether or not the collision is dangerous to occupants, on the basis of the variation with time. When it is dangerous, the comparator 3 generates a trigger signal which in turn triggers the drive circuit 4 as the one-shot multi-vibrator.
Therefore, the trigger signal, the pulse width of which is not sufficiently wide, fails to trigger the one-shot multivibrator 4. The occupant protecting device may be unable to protect the occupants in such a collisional accident.
Next, a power source circuit suitable for the occupant protecting devices including an air bag, for example, thus far described will be described. In the occupant protecting device, when the power line is accidentally disconnected, a power supply is interrupted. In the accident, the energy stored in the capacitor contained in the output side of the device must be effectively used, and the power source circuit must be reliable.
FIG. 8 is a circuit diagram showing a conventional power source circuit for an igniting device of a vehicle occupant protecting device.
In FIG. 8, reference numeral 61 designates a battery; 62, an ignition switch; 63, a controller; and 64, a DC power source for air-bag inflation.
In the DC power source 64, the battery voltage which is supplied from the battery 61 through the ignition switch 62 to the controller 63, is boosted by a DC--DC converter 65 to be applied through a resistor 66 to an output capacitor 67. As a result, the output capacitor 67 is charged with the boosted voltage.
The output capacitor 67 has a large capacity since it must supply a power to a squib 80.
In the circuit, block diodes 68a and 68b are provided to block a reverse current, and a diode 69 is provided to block the rush current into the output capacitor 67.
A diagnosis circuit 70 includes a CPU. A diagnosis power source 71 receives a voltage from a car-carried battery 61, and supplies a required power to the diagnosis circuit 70.
A backup capacitor 71a is connected to the input side of the diagnosis power source 71. The backup capacitor 71a has a smaller capacity than the output capacitor 67.
A storage portion 72 transfers data to and from the diagnosis circuit 70.
Collision detecting units 74 to 79 are mounted at required parts of a car body. Each collision detecting unit includes an acceleration switch for closing in response to a predetermined change of acceleration, and a resistor. The collision detecting unit 74, for example, is made up of an acceleration switch 74a and a resistor 74b.
A squib 80, mounted on a steering portion, serves as an igniting electrode for igniting a powder to inflate an air bag (not shown) provided in the steering portion.
A spiral cable 81, which is a flexible code wound around the steering shaft, connects the squib 80 to a controller 63 electrically. The spiral cable 81 and the squib 80 constitute an operation controller 80A.
In the figure, only one squib 80 is illustrated, but if required, a plural number of squibs 80 may be provided at other seats. In this case, those squibs are electrically arranged in parallel.
Reference numerals 73a to 73n designate output terminals of the controller 63. The output terminal 73a is connected to a line L1, through the collision detecting unit 74, output terminal 73b, output terminal 73e, spiral cable 81, squib 80, and output terminal 73f.
The output terminals 73h, 73j, 73l, and 73n are connected to a line L2.
The collision detecting unit 75 is connected between the output terminal 73a, 73c and 73d.
Similarly, the collision detecting units 76, 77, 78, and 79 are respectively provided between the output terminals 73g and 73h, the output terminals 73i and 73j, the output terminals 73k and 83, and the output terminals 73m and 73n.
The output terminals 73h, 73j, 73l, and 73n are connected to the line L2, which is grounded.
The diagnosis circuit 70, contained in the controller 63, is grounded through a connector harness 82 and a switch SW, and also through a connector harness 83 and an alarm lamp La.
The operation of the power source circuit thus arranged will be described.
When the ignition switch 62 is closed, the voltage supplied from the battery 61 is boosted by the DC--DC converter 65. The boosted voltage is applied through the diode 68c to the output capacitor 67. The capacitor 67 is charged with a time constant which is determined by the resistor 66 and the output capacitor 67. The voltage applied to the output capacitor 67 is always higher than the battery voltage from the battery 61.
Any of the acceleration switches 74a to 79a is placed to a state resembling a short-circuited state, and a voltage across the corresponding resistor of those resistors 74b to 79b takes a normal value, the diagnosis circuit 70 determines whether the cause bringing about such a state of the switch is the failure or the collision, and stores the result of the determination into the storage portion 72.
The storage portion 72 stores information on which of the acceleration switches 74a to 79a is turned on by the collision.
In the event of a collision with another vehicle, for example, a negative acceleration is generated, as a result of which any of the acceleration switches 74a and 75b and any of the acceleration switches 76a to 79a is turned on. The charge derived from the output capacitor 67 flows through a route as indicated by a broken line. The squib 80 is heated, the powder is fired, and the air bag is inflated.
A serious collisional accident occurs, and a large impact is applied to the diagnosis circuit 70. Even under such severe conditions, the diagnosis circuit 70 must operate normally in order that it can grasp a state of the air bag system correctly.
In the conventional power source circuit arranged described above, if the ignition switch 62 is disconnected from the controller 63 by the collision, the power supply to the diagnosis circuit 70 is interrupted. As a result, the diagnosis circuit 70 will be stopped in operation.
The diagnosis circuit 70 is not stopped at the instant that the disconnection occurs since the electrical energy is supplied from the backup capacitor 71a to the diagnosis circuit 70 for a preset time period after the disconnection. In this case, the time period of supplying the energy is a short time since the capacity of the backup capacitor 71a is small. To obtain a long time continuation of the energy supply, a large capacity must be used. Further, the disconnection also stops the power supply to the DC power source 64.
Thus, in the air bag system, the energy stored in the backup capacitor 71a is used for continuing the diagnosis operation of the diagnosis circuit 70 after the disconnection, for heating the squib 80 to ignite the powder and to inflate the air bag. In this respect, it is necessary to effectively utilize the energy in the backup capacitor 71a and the output capacitor 67.
Nevertheless, no measure for effectively utilizing the stored energy under the power interrupted condition has been taken.